Physiological monitoring systems include patient monitors and corresponding noninvasive sensors for measuring constituents of circulating blood. Such patient monitoring systems have gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care and neonatal units, general wards, home care, physical training and virtually all types of monitoring scenarios. A noninvasive sensor having light emitting diodes (LEDs) transmits optical radiation into a tissue site. A detector responds to the intensity of the optical radiation after absorption by pulsatile blood flow within the tissue site. Based upon this response, a patient monitor determines measurements for physiological parameters such as oxygen saturation, pulse rate and perfusion among others. Advanced patient monitors utilizing multiple wavelength sensors determine measurements for other physiological parameters, such as carboxyhemoglobin and methemoglobin, as examples.